In a process of manufacturing a semiconductor device or a liquid crystal display device, a plasma processing apparatus such as a plasma etching apparatus, a plasma CVD film forming apparatus or the like is used to perform a plasma process such as an etching process, a film forming process or the like on a target substrate (e.g., a semiconductor wafer or a glass substrate).
In recent years, for the aforementioned plasma processing apparatus, attention has been paid to the RLSA™ microwave plasma processing apparatus in which a planar antenna having a plurality of slots formed therein in a predetermined pattern is installed above a chamber, and microwaves introduced from a microwave source are emitted through the slots of the planar antenna and are radiated into the chamber being in a vacuum state via a dielectric microwave transmission plate installed below the slots. Gas introduced into the chamber by an electric field of the microwaves is changed to plasma so that a target object such as a semiconductor wafer or the like is processed.
Furthermore, a microwave plasma processing apparatus having a microwave plasma source, which distributes microwaves on a plurality of paths and introduces the microwaves into a chamber through a plurality of antenna modules having the planar antenna to spatially combine the microwaves inside the chamber, has also been proposed.
Such an apparatus includes a power feed port which is installed in a line extending along an axis of a waveguide having a coaxial structure such that an electromagnetic wave power such as a microwave power is supplied to the waveguide through the power feed port.
However, a power feeding method of the above conventional apparatus provides available power in a narrow range, which makes it difficult to supply power required for a microwave plasma processing apparatus.
On the other hand, a technique which feeds an electromagnetic wave power such as a microwave power to a waveguide of a coaxial structure through a coaxial line from a power introduction port by using a ring-shaped antenna, has been proposed. The power introduction port is installed in a lateral portion of the waveguide. This technique uses a microwave having a low frequency of about 860 MHz to supply more useful power in a wide range.
In recent years, there is a desire to supply power greater than that available in the conventional power feeding technique. To support this, a power combining technique is under consideration.
A Wilkinson combiner is known as such a power combining technique. However, in this technique, a reflection absorption resistor is installed inside a combiner, which inevitably increases the combiner in size. In addition, this technique employs a “direct supply” scheme (which transmits power as is). As such, a power loss is likely to occur, thus generating heat. This reduces an effectively transmissible power.
To address such problems, another power combiner has been proposed which includes: a plurality of power introduction ports; a plurality of power feeding antennas that are installed in the respective power introduction ports and radiate supplied electromagnetic waves into a main body; a combining part that spatially combines the electromagnetic waves radiated into the main body from the plurality of power feeding antennas; and an output port that outputs the electromagnetic waves combined by the combining part. Each of the power feeding antennas includes: an antenna main body equipped with a first pole to which the electromagnetic waves are supplied from the power introduction port and a second pole through the supplied electromagnetic waves are radiated; and a reflection part that is installed to laterally protrude from the antenna main body and reflects the electromagnetic waves. The power feeding antenna is configured to generate standing waves using the electromagnetic waves incident onto the antenna main body and the electromagnetic waves reflected at the reflection part. The electromagnetic waves as the standing waves radiated from the power feeding antennas are combined by the combining part.
Such a power combiner does not require an internal reflection absorption resistor, which achieves miniaturization and avoids the problem of heat generation.
In some instances, for transmission of microwaves, if a higher order mode other than a TEM mode is generated, a propagation characteristic of the microwaves may be degraded. Therefore, it is necessary to suppress the higher order mode as much as possible. However, the conventional power combiner fails to sufficiently suppress the generation of a higher order mode, which makes it difficult to combine microwaves of a high power with high efficiency.